Multiple-tuning type, differentialarrangement device for measuring reactances



Septl29, 1959 BUNJIRO ICHIJO 2,906,950

MULTIPLE-TUNING TYPE, DIFFERENTIAL-ARRANGEMENT DEVICE FOR MEASURINGREACTANCES Filed March 12. 1957 4 Sheets-Sheet l an-a Sept. 29, 1959BUNJIRO lCHlJO 2,906,950 MULTIPLE-TUNING TYPE, DIFFERENTIALARRANGEMENTDEVICE FOR MEASURING REACTANCES 4 Sheets-Sheet 2 Filed March 12, 1957llllllr Sept. 29, 1959 BUNJIRO ICHIJO 2,906,950

MULTIPLE-TUNING TYPE, DIFFERENTIAL-ARRANGEMENT DEVICE FOR MEASURINGREACTANCES Filed March 12, 1957 4 Sheets-Sheet 3 I I j 12 1' fig 8-Sept. 29, 1959 BUNJIRO ICIHIJO MULTIPLE-TUNING TYPE,DIFFERENTIAL-ARRANGEMENT Filed March 12, 1957 DEVICE FOR MEASURINGREACTANCES 4 Sheets-Sheet 4 R2 mm United States Patent ()fifice2,906,950 Patented Sept. 29, 1959 MULTIPLE-TUNING TYPE, DIFFERENTIAL-ARRANGEMENT DEVICE FOR lVIEASURING REACTANCES Bunjiro Ichijo,Hamamatsu-shi, Japan, assignor to K- kusai Denki Kabushiki Kaisha,Tokyo-to, Japan, a Japanese limited-liability company Application March12, 1957, Serial No. 645,572

Claims priority, application Japan March 19, 1956 Claims. (Cl. 324-61)This invention relates to a multiple-tuning type,differential-arrangement device for measuring reactances andparticularly to a device capable of directly measuring a static capacityof a test specimen in a precise manner without being influenced by theresistance of the said specimen.

Heretofore, the present invention has already proposed a Differentialcapacitance type device so constructed that it comprises detectorcircuit having two sets of identicallyconstructed andidentically-arranged L-C circuits and a pick-up coil, and so that, bythe adjustment of the capacity values of the said two L-C circuits sothat they assume symmetrical positions particularly on both sides,respectively, of the tuning point on the tuning or resonance curve, bythe connecting of the said detector circuits to an indicating meter sothat their output currents flow, respectively, in opposite directionsthrough the said indicating meter, and by the inserting of test specimenin two sets of electrodes connected inparallel to the said L-C circuits,the said device can be operated. However, since such a device issensitive to variations in frequency of the high frequency oscillator ofthe electrical source, the shifting of the Zero point can not be avoidedbecause of the infinitesimal frequency variations due to changes in theambient temperature. An essential object of the present invention is toeliminate elfectively the aforesaid disadvantage.

In order to attain the principal object, the device of the presentinvention is embodied in an infinitesimal-reactance-measuring devicewhich may be said to be of a multiple-tuning type in which one tuningcircuit is connected additionally, through a capacitance, to each of theaforesaid tuning circuits.- The resulting device has an extremely highdegree of measuring sensitivity and stability. By means of the deviceembodying the present invention, such conditions as moisture content andthicknesses of test specimens of such materials as textiles, papers canbe read directly, independentlyof such conditions as the characteristicsof the water or the temperature, through the variations in electrostaticcapacities or in inductances, and, furthermore, the electrostaticcapacities or the dielectric constants of semiconductors such as woods,textiles, and clays containing large quantities of water can bedetermined with precision.

The novel features of the invention can be better understood from thefollowing detailed description, when taken together with theaccompanying drawings, in which:

Fig. 1 is a schematic connection diagram explaining the principle ofthis invention.

Fig. 2 is a detailed connection diagram of one side only of Fig. 1.

Figs. 303) and 3 (D) are two kinds ofthe characteristic curvesindicating the relations between the indicator currents I I a and thecapacitance of the variable capacitors C2, C26! in 1.

Figs. 3(A) and 3(0) are diagrams of two kinds of th characteristiccurves indicating the relationsbetween the currents I I a of the tuningcircuits and the variable capacitors C C 11 in Fig. 1.

Fig. 4 is a diagram of characteristic curves indicating the relationsbetween the variation AC of the variable capacitor C and indicatorcurrent l in Fig. 1.

Fig. 5 is a diagram of characteristic curves indicating the relationsbetween the indicator currents I and the values of the resistance R inFig. 1.

Fig. 6 is a diagram of a characteristic curve indicating the relationbetween the indicator current I and the water content M of a testspecimen.

Fig. 7 is a connection diagram of another example of this invention, forexplaining the method of inserting the test specimen when the moisturecontent of such a material as fabric or paper is to be measured.

Fig. 8 is a plan and side view of a modification of an electrode,assemblage in this invention, for supporting a test specimen.

Fig. 9 is a diagram of characteristic curves indicating the relationsbetween the indicator currents I I a and the capacitances of thevariable capacitors C C a in Fig. 1, in the case of adoption of analternative method suitable for the measurement of the capacitance of asemi-conductor.

In Fig. 1, the device includes an oscillator 1 with stabilizedfrequency, two sets of first tuning circuits 2 and 2a which are coupledelectro-magnetically or electrostatically to the tank circuit of thesaid oscillator 1 and pick-up coils 3 and 3a which are coupled to thesaid tuning circuits 2 and 2a, respectively. The high-frequency currentsinduced in the said pick-up coils are rectified by crystal or germaniumrectifiers 4 and 4a, respectively, and flow through an indicator 5 inmutually opposite directions. Two sets of second tuning circuits 6 and6a which are coupled electro-statically to the aforesaid first tuningcircuits 2 and 2a, respectively, through capacitor C and C al withinfinitestimal capacitances, respectively. Test specimens 7 and 7a whichare to be measured are connected in parallel with capacitors C and C a,respectively, each of the said capacitors being one of the seriescapacitors CS0, C and C a, C arespectively.

In the carrying out of a measurement by the device as described above,the tuning circuits 2 and 2a are adjusted at a time in the followingmanner. First, the switch S is closed, and the capacitor C is adjustedso as to cause the current of the tuning circuit 2 to be at its maximumvalue. Next, the switch 8 a is closed, and the capacitor C a issimilarly adjusted so as to cause the current of the tuning 7 equal.Next, if the switch S is opened, and the capacity of thevariablecapacitor C is varied, the relation between the capacitance of thecapacitor C and the indicator current I will vary as indicated by thefull line of Fig 3(B). However, if the capacitance of the capacitor C isincreased by AC from the minimum current position and set at the point0, the current I will become 0A If, atthis' point, the capacitor C ofthe first tuning circuit 2 is readjusted, and the multiple tuningcircuit comprising the tuning circuits 2 and 6 is tuned, the saidcurrent will increase from 0A to 0A. In this case, the current I of themultiple tuning circuit will change from the full line of Figs. 3(A) and3(B) to the dotted line.

Similarly, if the capacitance of the capacitor C a is reduced by AC fromthe minimum current position and set at point 0 the current I a willbecome O B and, through the readjustment of the condenser C a, the current will become 0 B (see Fig. 3(D)). In this case, the current I a ofthe multiple tuning circuit will change from the full line of Figs. 3(C)and 3(D) to the dotted line. However, because these currents I and I aflow in mutu.

ally opposite directions through the indicator 5 and mutually suppresseach other, even if their values are of the order of milliamperes,micro-ammeters of high sensitivity can be used as the indicating meter,and the sensitivity of the entire device will become extremely good.Then, if the specimens 7 or 7a to be measured is connected in parallelto C or C a, the capacitance increase of the circuit 6 or 6a will becomewhere C' ac and the point A will shift to A and the point B to B in Fig.3. Consequently, the output current corresponding to this AC; willbecome A1 or Al of Fig. 3(8) and Fig. 3(D); as a result, the indicatingmeter can be made to swing through a large angle.

Fig. 2 is indicated only one side of the circuit of Fig. 1, in which thesame members are indicated by the same numerals. If, in this case, thedetecting characteristic of the rectifier 4 is taken to conform to thesquare law characteristic, the current I will be given by the followingequation. 0 R

a 0 1+ 2 2 2 z I =.KE =I(w Zll-e-w C R Xmm where,

K=a proportional constant :induced voltage in the pick-up coil 3e=induced voltage from the oscillator in the first tuning coil 2 w=21rf,in which 1 is the frequency M :mutual inductance between the circuit 2and the coil 3 R =resistance of the first tuning circuit 2 R =resistanceof the second tuning circuit 6 C =capacitance of the first tuningcircuit 2 C =capacitance of the coupling C Then, the value of wACR forwhich Equation 4 becomes a maximum is Therefore, when wACR =i1 inEquation 5,

As a result, it can be seen with the present circuit ar-.

rangement that the requisite condition for maximum vari-. ation,corresponding to the infinitesimal capacitance variation of 2nd resonantcircuit, of the indicating ammeter and the requisite condition for theswing of the indicating pointer of the indicating arnrneter to becomezero for the infinitesimal variation of the resistance R are coincident.This is the most significant special feature of the circuit arrangementembodying the present invention. The said feature cannot be obtained inthe directreading capacitance meters existing hitherto.

In Figs. 4, 5 and 6 are shown drawings illustrating an example of anactual experiment showing the aforesaid relations. Fig. 4 indicates therelation of the variation of AC to the indicator current I Fig. 5indicates the fact that, under the condition for maximum indicatingcurrent, that is, for wA"R =l, and within the range of 200 to 500 K!) ofthe value of the resistance R the indicated current I without beinginfluenced by variations in the resistance R becomes almost constant.Fig. 6 illustrates an example of an actual experiment in the measurementof the water content M of a test specimen and indicates the fact thatthe result of the said measurement is not influenced by the thickness t,that is, the resistance, of the said test specimen.

When the present device is to be used as only a directreadingcapacitance meter, either the specimen 7 or 7a of Fig. 1 becomes thespecimen C to be measured. However, when the present device is to beused as an instrument for measuring moisture content, either thespecimen 7 or 7a in Fig. 1 may be made the specimen to be measured; or,as illustrated in Fig. 7, the electrodes 8 and 9 having a commongrounded electrode 10 may be connected to the circuits 6 and 6a, and thetest specimen 11 may be inserted between the said electrodes and moved.Rod-shaped electrodes 12, 13 and 14 in grill assemblage as illustratedin Fig. 8 may be used, and the test specimen 15 may be moved over, andin contact with, the electrodes.

In the measurement of the thickness of a specimen, the measurement canbe made by the variation of the infinitesimal inductance of the coil ofthe circuit 6 or 611. That is, if the specimen to be measured is placedbetween the surface of the said coil and a metal plate, the variation ALof the coil industance L will be indicated as AL=LK wherein K is thecoupling coefiicient of the said coil and the said metal plate andvaries with variation of the distance between the said coil and the saidmetal plate, that is, with the thickness of the said specimen.Therefore, the value of AL, that is, the magnitude of the variation ofcurrent, will indicate directly the thickness. Consequently, in thiscase, for substances or materials other than metals, the thicknesses ofthe materials can be measured on the same calibration scale, regardlessof their respective electrical properties.

Next, another method suitable for precise measurement, by means of adevice embodying the present invention, of the electro-static capacitiesor the dielectric constants of semi-conductors, for example, woods,textiles, clays, etc., containing a large quantity of water, will bedescribed in the following explanation.

In this method, with reference to Fig. 1, the capacitors C and C a areshorted, the capacitors C and C a are removed, and the test specimens Chaving equivalent parallel resistance R and which are inserted betweentwo electrodes of identical construction, are directly connected inparallel, through the switches S and S a, respectively, to the secondtuning circuits 6 and 6a, respectively. Then, the switch S is firstclosed; the capacitor C is adjusted; the meter 5 is made to indicatemaximum reading; and the degree of coupling with the electrical sourceis adjusted so that the current I under these conditions is in the orderof some milliamperes. Next, the switch S is opened; the capacitor C isadjusted; then the relation between the value capacitance of thecapacitor C and the current I will become that as indicated by theV-shaped curves shown in Fig. 9. Each of these curves is geometricallyquite symmetrical about the ordinate line for the capacitance of thecapacitor C corresponding to the minimum value of the current, I thatis, C regardless of whether the sign of the variation AC of thecapacitance C is positive or negative.

*3 The adjustments with respect to capacitors Cga and a are carried outin a similar manner. When the values of the capacitances of thecapacitors C and C 4 of these two tuning circuits are to be set at C,,,;+AC, and C AC, respectively, the currents I and I a .of the upperand lower sets of circuits become the values indicated by the points Aand B, respectively, on the curve Ru:- Since these values are equal, thereading of the meter 5 will be zero. This completes the initialadjustment.v

Next, if the switches S and 5 a are closed, and the test specimens C areinserted simultaneously in both circuits, the point A, in accordancewith the resistance value of the test specimen, will move in a mannersuch as that to A A or A even for the same capacitance of the specimen Cand the point B will move as that to B B B However, in Fig. 9, themovements A A and B B are those for the case when the specimenresistance is infinity, that is, R,,,. Also R R As one illustrativeexample, if it is assumed that the circuit resistance becomes R becauseof the test specimen, the output current becomesA B that is, a b becausethe point A moves to A and the point B moves to B Then, if thecapacitance value of the capacitor C is gradually decreased, theindication of the meter will gradually decrease until it finally becomeszero. That is, if the capacitance value of the capacitor C is decreasedalong B b point a will be obtained as the point of intersection with thecurve R However, points A and a represent currents of equal value and,at the same time, the curves are symmetrical with a centerline formed bythe ordinate line through the capacitance 0 Therefore, in this case, thecapacity variation represented by B b corresponds exactly to ZCConsequently, the capacitance value of specimen C can be read directlyfrom the reading on the dial of the capacitor C By the use of thismeasuring method, as can be understood from Fig. 9, the capacitance ofthe specimen C can be measured independently of the value of theresistance of the resistor R Moreover, because the curves in theirzero-current regions are sloped considerably, the precision ofmeasurement is increased. At the same time, because of the differentialtype of arrangement, a microammeter of high sensitivity can be used asthe indicator, and capacitances can be measured, thereby, with extremelyhigh precision.

The foregoing examples of practical application are merely examplespresented for explaining the principle of the present invention and foran understanding of its applications. It should be understood that thepresent invention is not limited to the aforementioned examples ofpractical applications, but is capable, within its stated scope, ofbeing useful in several forms and variations thereof.

I claim as my invention:

1. A multiple-tuned differential system for measuring a physicalcharacteristic or condition which is accurately proportional to a changeof reactance or impedance produced by it in the system and reflected asa signal to indicate the change comprising, in combination; a stabilizedhigh-frequency oscillator; a first pair of separate tuning circuitsindividually coupled to said oscillator; a second pair of tuningcircuits each electrostatically, and serially coupled to a respectivecircuit of said first pair of tuning circuits; a pair of pick-up coilseach electromagnetically coupled to a respective circuit of said firstpair of tuning circuits; indicating circuits differentially connected tosaid coils to detect and indicate current flow induced in said coils;means connected to said differentially connected cir cuits forindicating the value of the current flow which is representative of thephysical characteristic or condition to be measured, means includingvariable tuning capacitors connected in said tuning circuits foradjustably causing the indicating means to indicate zero current flow inpreparation for a measurement; and circuit means including testelectrodes electrostatically coupled to said second pair oftuningcircuits for connecting at least one specimen in parallelwith saidsecond pair of tuning circuits thereby to measure a physicalcharacteristic or condition thereof and indicate the value thereof onsaid indicating means.

2. A multiple-tuned differential system for measuringaphysicalcharacteristic or condition which is accurately proportional'toa change of reactance or impedance produced by it in the system andreflected as a signal to indicate the change comprising, in combination;a stabilized, high-frequency oscillator; a first pair of separate tuningcircuits individually electromagnetically coupled to said oscillator; asecond pair of tuning circuits each electros'tatically,and seriallycoupled to a respective circuit of said first pair of tuning circuits; apair of pick-up coils each electromagnetically coupled to a respectivecircuit of said first pair of tuning circuits; indicating circuitsdifferentially connected to said coils to detect and indicate currentflow induced in said coils; means connected to said differentlyconnected circuits for indicating the value of the current flow which isrepresentative of the physical characteristic or condition to bemeasured, means including variable tuning capacitors connected in saidtuning circuits for adjustably causing the indicating means to indicatezero current flow in preparation for a measurement; and circuit meansincluding test electrodes electrostatically coupled to said second pairof tuning circuits for connecting at least one specimen in parallel withsaid second pair of tuning circuits thereby to measure a physicalcharacteristic or condition thereof and indicate the value thereof onsaid indicating means.

3. A multiple-tuned differential system for measuring a physicalcharacteristic or condition which is accurately proportional to a changeof reactance or impedance produced by it in the system and reflected asa signal to indicate the change comprising, in combination; astabilized, high-frequency oscillator; a first pair of separate tuningcircuits individually electrostatically coupled to said oscillator; asecond pair of tuning circuits each electrostatically, and seriallycoupled to a respective circuit of said first pair of tuning circuits; apair of pick-up coils each electromagnetically coupled to a respectivecircuit of said first pair of tuning circuits; indicating circuitsdifferentially connected to said coils to detect and indicate currentflow induced in said coils; means connected to said differentiallyconnected circuits for indicating the value of the current flow which isrepresentative of the physical characteristic or condition to bemeasured, means including variable tuning capacitors connected in saidtuning circuits for adjustably causing the indicating means to indicatezero current flow in preparation for a measurement; and circuit meansincluding test electrodes electrostatically coupled to said second pairof tuning circuits for connecting at least one specimen in parallel withsaid second pair of tuning circuits thereby to measure a physicalcharacteristic or condition thereof and indicate the value thereof onsaid indicating means.

4. A multiple-tuned differential system for measuring a physicalcharacteristic or condition which is accurately proportional to a changeof reactance or impedance produced by it in the system and reflected asa signal to indicate the change comprising, in combination; astabilized, high-frequency oscillator; a first pair of separate tuningcircuits individually coupled to said oscillator; a second pair oftunning circuits each electrostatically and serially coupled to arespective circuit of said first pair of tuning circuits; capacitorsindividually coupling each of said second pair of tuning circuits tosaid first pair of tuning circuits; each of said capacitors being of aninfinitely small capacitance; a pair of pick-up coils eachelectromagnetically coupled to a respective circuit of said first pairof tuning circuits; indicating circuits differentially connected to saidcoils to detect and indicate current flow induced in said coils; meansconnected to said differentially connected circuits for indicating thevalue of the current fiow which is representative of the physicalcharacteristic or condition to be measured, means includ-' ing variabletuning capacitors connected in saidtuning circuits for adjustablycausing the indicating meansto indicate zero current flow in preparationfor a measurement; and circuit means including test electrodeselectrostatically coupled to said second pair of tuning circuits forconnecting at lease one specimen in parallel with said second pair oftuningv circuits thereby to measure a physical characteristic orcondition thereof and'indi'cate the value thereof on said indicatingmeans.

5. A multiple-tuned differential system for measuring a physicalcharacteristic or condition which is accurately proportional to achange of reactance or impedance produced by it in the system andreflected as a signal to inclicate the change compirsing, incombination; a stabilized, high-frequency oscillator; a first pair ofseparate parallel tuned circuits individually coupled to saidoscillator; a second pair of parallel tuned circuits eachelectrostatically and serially coupled to a respective circuit of saidfirst pair of tuning circuits; a pair of pick-up coils eachelectromagnetically coupled to a respective circuit of said first pairof tuning circuits; indicating circuits difierentially connected to saidcoils to detect and indicate current flow induced in said coils; meansconnected to said differentially connectedcirc'uits for indicating thevalue of the current flow which is representative of the physicalcharacteristic or condition: to be measured, means includingvariable'tuning capacitors connected in said tuned circuitsforselect'ively, adjustably causing the indicating means to indicatezero current flow in preparation for a measurement; and circuit meansincluding test electrodes electro-, statically coupled to said secondpair of tuning circuits for connecting at least one specimen in parallelwith said second pair of tuning circuits thereby to measure a physicalcharacteristic or condition thereof and indicate the value thereof onsaid indicating means.

References Cited in the file of this patent UNITED STATES PATENTS

